TERI's enhanced acidification and methanation technology

Spelling 'waste' as 'wealth'

Food is the last thing that comes to mind when one sees rotting and stench-emanating landfills, overflowing with garbage from all over the city. Not surprising then that many will be shocked if they were told that it is an important source in the making of cooking gas.

Of late, there have been experiments to convert the emissions from landfills or garbage dumps to energy so as to power various applications. Though technologies exist, they are crippled with inefficient output and operational problems. The TEAM (T ERI's enhanced acidification and methanation) technology not only overcomes existing shortcomings but also promises to be an important parallel source of fuel for thermal applications, especially cooking.

Distilling the fuel of the future

Figure 1 Managing the ever-increasing waste

Tackling mounting waste (produced as a result of growing urbanization and industrialization) has been one of the biggest civic concerns in modern times (Figure 1). Working towards finding a sustainable solution, researchers at TERI zeroed in on biomethanation as the most desirable alternative for the treatment of solid waste, as it yields biogas that can replace conventional fuels and provides digested sludge that can be used as organic manure.

TERI's research culminated in the development of a high-rate digester for fibrous and semi-solid organic waste. The technology has been put to use in the waste treatment plant in TERI's sustainable habitat campus in Gurgaon, Haryana (Figure 2). The plant has been generating good-quality biogas and manure from organic wastes since the year 2000.

The innovation

Figure 2 The TEAM process

The TEAM process goes through a clean and structured scheme of things (Figure 3). Organic solid waste is cut into small pieces and fed into the acidification reactor. The waste bed is kept submerged in water. Organic acids formed as a result of bed degradation lead to the formation of leachate. This leachate is periodically recirculated through the bed at a predetermined fixed rate to have uniform concentration of microorganisms and nutrients through the bed and to wash off organic acids formed as a result of further bed degradation.

Once a high COD (chemical oxygen demand) concentration is reached, the leachate is extracted in the leachate collection tank. The acidification phase has a retention time of six days; therefore, six such reactors are provided to ensure continuous operation. Anaerobic conditions prevail inside the reactor during the whole process. The phase separation provides suitable environment to the microorganisms in acidification and methanation stages, thus enhancing the activity. (Figure 4). The residue inside the acidification reactor is dried in the sun and then used as manure (Figure 4).

Figure 3 Granules of microorganisms used to generate energy

Figure 4 Manure generated after processing waste

The final concentrated leachate, after pH correction, is fed into the UASB (upflow anaerobic sludge blanket) reactor for methanation. This phase has a retention time of 16 hours. The microbial consortia present in the UASB sludge destroys 90% of the COD, and forms biogas that comprises 70%–75% methane (a high calorific value fuel), carbon dioxide, nitrogen, traces of hydrogen sulphide, and moisture. The biogas production rate is 0.45 m3/kg COD reduced.

Figure 4 Waste being fed into the
acidification module

The final concentrated leachate, after pH correction, is fed into the UASB (upflow anaerobic sludge blanket) reactor for methanation. This phase has a retention time of 16 hours. The microbial consortia present in the UASB sludge destroys 90% of the COD, and forms biogas that comprises 70%–75% methane (a high calorific value fuel), carbon dioxide, nitrogen, traces of hydrogen sulphide, and moisture. The biogas production rate is 0.45 m3/kg COD reduced.

Beneficiaries

The TEAM technology can turn organic waste dumps into resource centres and tremendously ease the burden on cities, towns, and even villages. The technology will be of great relevance to municipal corporations as the TEAM process is an effective and ecological way of utilizing waste (Figure 6). Sectors that generate organic waste in large amounts – such as food and fruit processing industries, hotels, community kitchens, and vegetable markets – can make the best use of the technology. Other waste generating activities such as coffee processing, tea processing, and poultry farming will also benefit tremendously.

Applications/benefits

The TEAM process completely eliminates engineering problems such as scum formation, floating of feed material (it leads to incomplete digestion, blocking of inlet and outlet pipes, and difficulty in feed flow, which are common in small-scale plants. The process is better than the conventional single-phase reactors primarily due to low retention time with high treatment efficiency. Maintenance and operations are easy because there is no need for mixing and slurry preparation. Also, the process uses less water as it recycles treated liquefied waste for further extraction.

On the socio-economic front, the TEAM process generates employment; it is enterprise-friendly and suitable for small-scale units. It can also create work avenues for raw material suppliers. The cost of the plant depends on the composition of feedstock to be treated. For mixed feed, the cost is about 20 000 rupees per cubic metre. Payback period is less than two years.

The biogas produced through this process can be piped and put in use as domestic fuel, and also be used for thermal application and power generation.